General Motors' Hummer has both a fuel economy problem and an image problem. The brand's best-known model, the full-size H2, not only drinks a lot of gas, it really looks like it does.

GM has long talked of changing Hummer's image by introducing smaller models and has even considered an off-road capable hybrid Hummer. But the company has recently announced it may simply sell the brand.

EPA fuel economy estimates for the big Hummer H2, the brand's iconic model, aren't available because vehicles of its weight aren't actually considered "passenger vehicles," officially speaking. The H2 is therefore exempt from rules requiring the posting of fuel economy estimates.

For the first four months of this year, H2 sales are down almost 27 percent. Fewer than 3,000 H2's have been sold so far this year, compared to more than 4,000 by this time last year, according to data from the industry newspaper Automotive News.

Sales of the smaller Hummer H3 have been hurt even more. Sales of mid-sized truck-based SUVs, like the H3, have been declining even longer than sales of full-sized SUVs as buyers switch to smoother-riding, more efficient car-based crossovers. The H3 gets about 15 mpg in combined city and highway driving, which is relatively poor compared to similar vehicles of its size. H3 sales have dropped about 30 percent so far this year compared to last year.